Fabrics made of a regenerated cellulose fiber have had problems in that they have a tendency of creasing in grey and retaining the wrinkles generated in a wet condition (e.g. scouring), even after the drying step (a finishing step), giving a product fabric of very low quality.
In order for a product fabric not to generate wrinkles, measures are taken such as scouring and dyeing of fabric in rope form in bath containing softener, levelling agent or the like or scouring and dyeing of fabric in open width.
In order for a product fabric not to generate wrinkles during laundering, resin finish is applied to a fabric after dyeing. This treatment, however, have various problems; for example, the product fabric has a hard hand and a reduced strength.
A fabric which is being developed recently and which is made of a cellulose fiber obtained by spinning with an organic solvent, i.e. a lyocell fiber, generates wrinkles even after ordinary scouring in open width and gives heavy wrinkles after scouring in a rope form. These wrinkles generated in this fabric are not at all improved even when the fabric is dried under tension after the scouring. Thus, the conventional lyocell fiber has a large problem in practical application. JP-A-6-306733 discloses a process for producing a fibrillated fiber from an easily fibrillatable fiber, as an example of which a lyocell fiber is cited, by subjecting the latter fiber to a rubbing treatment in a solution containing a swelling agent for the fiber. The swelling agent includes an aqueous alkali solution (e.g. an aqueous sodium hydroxide solution). The rubbing treatment refers to rubbing a fabric in a rope form by the use of a machine such as washer (low-pressure type), continuous relaxing machine, jet dyeing machine, air flow dyeing machine, winch dyeing machine or the like. In such a treatment, reduction in fiber strength and generation of wrinkles are inevitable. JP-A-7-157968 discloses a rubbing treatment in an aqueous solution containing 60 g/l of sodium hydroxide by the use of a jet dyeing machine. This treatment is intended to rub a fabric in a rope form to form friction marks.
WO 95/24524 discloses mercerization of a fabric made of a lyocell fiber. In this mercerization, the fabric is treated in an aqueous solution containing a high concentration (10-30% by weight) of sodium hydroxide under tension. This mercerization is intended to improve the appearance of a lyocell fiber, particularly the condition of a fabric surface looking covered with frost due to friction mark. This mercerization, however, allows the resulting fabric to have a reduced tenacity and to invite generation of wrinkles after dyeing or during laundering.
The wrinkles generated in a fabric after dyeing or in a product fabric during laundering refers to the wrinkles generated in a fabric in a wet condition or in the transition period from a wet condition to a dry condition.
Generation of wrinkles is more frequent in viscose rayon than in cuprammonium rayon. However, when a tension is applied in open width in order to eliminate the wrinkles generated in a wet condition, in a drying step, the tension may be smaller in viscose rayon than in cuprammonium rayon. That is, viscose rayon generates wrinkles in a wet condition more easily but the wrinkles can be removed more easily. Conventional regenerated cellulose fibers typified by these viscose rayon and cuprammonium rayon have a low tenacity and a high elongation.
In contrast, in conventional lyocell fibers, the wrinkles are difficult to eliminate because the fibers have a poor balance between tenacity and elongation in a dry condition. In order to eliminate the wrinkles of a fabric made of a conventional lyocell fiber, it is considered effective to change the tenacity-elongation balance in a dry condition to a balance such as possessed by viscose rayon. However, in order to utilize the high tenacity possessed by a lyocell fiber, it is most desirable to change a lyocell fiber so as to have a high tenacity and a high elongation while reduction in tenacity is minimized.